In the prior art applicant is aware of U.S. Pat. No. 1,524,503, which issued Jan. 27, 1925 to Bennett et al for Trailer Coupling, U.S. Pat. No. 1,552,620, which issued Sep. 8, 1925 to Knox for Trailer Coupling, U.S. Pat. No. 2,460,466, which issued Feb. 1, 1949 to Nogle for Trailer Dolly, U.S. Pat. No. 2,360,902, which issued Oct. 24, 1944 to Simmons for Vehicle, U.S. Pat. No. 1,957,917, which issued May 8, 1934 to Storey for Tractor, U.S. Pat. No. 3,298,706, which issued Jan. 17, 1967 to Lyall for Heavy Motor Vehicles and Equipment, U.S. Pat. No. 1,643,885, which issued Sep. 27, 1927 to Gill for Means for Loading and Hauling Automobiles.
Knox and Bennett describe trailer coupling assemblies using two vertically aligned hitch points for the purpose of automatically elevating a trailer while connecting the trailer to the tow vehicle in order to transfer trailer weight to the rear axle of the tow vehicle.
Nogle discloses a wheeled dolly having two horizontally aligned connecting points to carry the weight of the front of a trailer towed behind the dolly.
Simmons describes providing one or more connection points for the purposes of selectively transferring weight from one portion of the vehicle to another and to change the angular alignment of the interconnected vehicles.
Storey discloses providing articulation to interconnect two parts of a vehicle. Applicant is aware that in the prior art it is known to provide booster axles designed to be attached to the front or rear of vehicles for the purpose of transferring weight from the vehicles to the booster axles to increase the carrying capacity of the vehicles.
By way of example, Lyall describes an articulating booster axle designed to transfer part of a crane's weight to a booster axle that trails or tracks behind the crane.
Gill teaches an automobile carrier with a hitch assembly located aft of the truck frame.
Applicant has in the present invention improved on his invention described and claimed in his United States patent application entitled Roll coupling Trailer Hitch Assembly, filed Jul. 14, 2008, and published Jan. 15, 2009, under publication number US2009-0014982.
As commercial vehicles increase load capacity by increasing the number of weight bearing axles over a given length, the vehicle's centre of gravity is raised and the vehicle becomes increasingly unstable while in motion. In applicant's experience, the governing governmental authorities have started to restrict weights on combination vehicles where the trailers are attached to the rear of tow vehicles (including dump truck and pony trailer combinations, or other truck and trailer combinations, or combinations where a trailer is towed by another trailer) in order to reduce the number of accidents involving these vehicles.
In applicant's experience, at least with respect to truck and trailer combinations, roll coupling these types of vehicle combinations may improve safety and provide an alternative to reducing weight limits by the governing authorities. To the knowledge of applicant, tridem (that is, three axle) pony trailers are presently limited to 21,000 kgs on the trailer axles in British Columbia, Canada. The previous maximum weight for a tridem axle group in British Columbia was 24,000 kgs.
Roll coupling may provide improved yaw and roll stability where there is roll coupling between the tow vehicle and towed trailer when used in conjunction with sufficiently torsionally strong draw bars and corresponding supporting framework on the trailer to resist twisting during initial rolling motion of the trailer and so as to import the resulting torque to the roll coupling and thence to the tow vehicle. A single roll coupling hitch or a plurality of diagonal, horizontal or vertically aligned hitch assemblies and contact points may be used as required for different applications to provide roll coupling and so as to allow legal hitch offset distances, and so as to provide redundant critical hitch components and so as to reduce operating stresses on individual hitch components. Using common hitch components whenever possible also enables the tow vehicle to be used with trailers equipped with lunette rings, that is, which are not equipped with roll couplers.
A dynamic analysis was conducted to simulate the performance of roll coupling utilizing the University of Michigan Transportation Institute (UMTRI) yaw/roll model for a tandem truck/tridem pony trailer for the following four conditions: Loaded truck (GVW 26 100 kg), loaded trailer (GVW 21 000 kg)—no roll-coupling; Empty truck (GVW 13 695 kg), loaded trailer (GVW 21 000 kg)—no roll-coupling; Loaded truck (GVW 26 100 kg), loaded trailer (GVW 24 000 kg)—roll-coupling; and, Empty truck (GVW 13 695 kg), loaded trailer (GVW 24 000 kg)—roll-coupling.
The truck trailer dimensions are summarized in Table 1. Loads were placed on the truck and trailer so that the maximum axle group loads were achieved at maximum legal height (4.15 m).
TABLE 1Summary of truck/trailer dimensionsParameterDimension (m)TruckWheelbase6.109Drive group spread1.397Hitch offset1.448Hitch height0.591TrailerWheelbase6.464Trailer group spread2.769Deck height0.864
The following performance measures were evaluated for each load condition. The performance measures are described below. Handling performance—oversteer transition (H-P1); Handling performance—understeer coefficient at 0.3 g (H-P2); Handling performance—understeer coefficient at 0.15 g (H-P3); Handling performance—understeer coefficient at 0.25 g (H-RTAC); Static rollover threshold (SRT); Load transfer ratio (LTR); Rearward Amplification (RA); Lateral friction utilization (LFU); Friction demand (FD); Low-speed off-tracking (LSOT); High-speed off-tracking (HSOT); Transient off-tracking (TOT).
The simulation results are summarized in Table 2.
The handling performance of the loaded truck/pony trailer was improved with roll coupling. The degree of oversteer occurring at high lateral accelerations was reduced and the transition from understeer to oversteer occurred at a higher lateral acceleration when roll coupling was present. The handling performance was essentially the same for both the non roll coupled and roll coupled trailers in combination with an empty truck. However the roll coupled trailer exhibited less understeer and therefore has slightly improved handling characteristics.
TABLE 2Simulation ResultsTandem truck/Tridem pony trailerNon-rollNon-rollRollRollcoupledcoupledcoupledcoupledPerformanceLoadedEmptyLoadedEmptyPerformance MeasuresStandardTruckTruckTruckTruckHandling performance>0.20g's0.2090.37302170.318(point #1)Oversteer transitionHandling performance>−4.45deg/g−4.081 0.671−3.175 0.339(point #2)USC at 0.3 gHandling performance>0.50, <2.00 deg/g0.9612.6271.5152.049(point #3)USC at 0.15 gHandling performance>−4.45deg/g−2.171 2.530−1.159 1.439(RTAC)USC at 0.25 gStatic rollover threshold>0.35g's0.3480.4100.3720.513Load transfer ratio<0.600.7250.7090.5240.510Rearward amplification<2.001.9922.0111.7281.841Low-speed lateral<0.800.4570.3620.5320.396Friction utilization (lowfriction)Friction demand<0.100.1850.4410.1910.424Low-speed offtracking<5.60m2.4832.3412.5912.468High-speed offtracking<0.46m0.5590.3300.4950.374Transient offtracking<0.80m0.5710.5180.4920.423Load Height - truck (m)4.15 2   4.15 2   Load Height - trailer (m)4.15 4.15 4.15 4.15 Steering axle load (kg)9 100    5 665    9 100    5 665    Drive Group load (kg)17 000    8 030    17 000    8 030    Trailer load (kg)21 000    21 000    24 000    24 000    Gross Combination Weight (kg)47 100    34 695    50 100    37 695    
Stability was improved under both loading conditions with roll coupling, enabling the static rollover performance standard of 0.35 g to be achieved when coupled with a loaded truck.
Roll coupling resulted in an improvement dynamic performance for all dynamic performance measures (that is, LTR, RA, and TOT as defined below). The use of roll coupling allowed all the dynamic performance standards to be achieved under both loading conditions. Of particular note is the significant improvement in load transfer ratio in the order of 28% under both loading conditions.
The low-speed performance was largely unaffected by roll coupling. However this configuration exhibited high levels of friction demand (FD) with and without roll coupling, particularly when the truck was unloaded. This implies that only a loaded truck should be used to haul a loaded trailer under low traction conditions. Even with a loaded truck care should be taken when negotiating tight turns.
The high-speed offtracking performance standard (<0.46 m) was achieved for both coupling methods when hauled by an empty truck. The standard was not achieved for either coupling method when hauled by a loaded truck, but performance was marginally better with a roll coupled trailer.
Understeer Coefficients (USC) were used to evaluate handling performance at steady-state conditions by calculating the understeer coefficient at 0.15 g, 0.30 g, (TAC 0.25 g). This measure is expressed in degrees per g which represents the slope of the handling diagram. Positive and negative values indicate understeer and oversteer levels respectively. This performance measure is determined during a ramp steer manoeuvre (ramp steer rate of 2 deg/sec at steering wheel) at a forward velocity of 100 km/h. The pass/fail criterion is addressed by comparing the understeer coefficient with the critical understeer coefficient, which can be expressed as −Lg/U2, where U is the vehicle speed (U=27.77 m/s (100 km/h)), L is the tractor or truck wheelbase (in meters), and g is acceleration due to gravity (9.81 m/s2). If the value of the understeer coefficient is greater than the critical value, the vehicle will meet the criterion (TAC performance standard). In addition the lateral acceleration where the transition from understeer to oversteer (that is, the point where the understeer coefficient is zero) is also computed.
Static Rollover Threshold (SRT) is the level of steady lateral acceleration beyond which the configuration rolls over. The measure is expressed as the lateral acceleration (in g's) at which all wheels on one side, except the steer axle, lift off the ground. Configuration performance is considered satisfactory if the static rollover threshold is greater than or equal to 0.35 g.
Load Transfer Ratio (LTR) is defined as the ratio of the absolute value of the difference between the sum of the right wheel loads and the sum of the left wheel loads, to the sum of all the wheel loads. The front steering axle is excluded from the calculations because of its relatively high roll compliance. Configuration performance is considered satisfactory if the LTR is less than or equal to 0.60 (TAC performance standard). This performance measure is evaluated during a rapid lane change manoeuvre conducted at 88 km/h, yielding a lateral acceleration amplitude of 0.15 g and a period of 2.5 seconds at the tractor's steering axle.
Rearward Amplification (RWA) is defined as the ratio of the peak lateral acceleration at the mass centre of the rearmost trailer to that developed at the mass centre of the tractor. Configuration performance is considered satisfactory if the RWA is less than or equal to 2.0, which is the current TAC performance standard. This performance measure was evaluated in the same manoeuvre as LTR.
Friction Demand (FD) performance measure describes the non-tractive tire friction levels required at the drive axles of a tractor. Excessive friction demand is a contributing factor to jack-knife and also results in excessive tire wear. Friction demand is the absolute value of the ratio of the resultant sheer force acting at the drive tires divided by the cosine of the tractor/trailer articulation angle to the vertical load on the drive tires. Configuration performance is considered satisfactory if FD is less than or equal to 0.1 (TAC performance standard). This performance measure is evaluated in a 90-degree turn at a vehicle speed of 8.25 km/h. During the manoeuvre, the centre of the front steer axle tracks an arc with a 12.8-m radius (approximately a 14-m outside-wheel-path radius).
Lateral Friction Utilization (LFU) is a measure proposed by NRC to characterize the highest level of the lateral friction utilization at the steering axle. LFU is defined as the ratio of the sum of lateral forces to the vertical load, and the peak tire/road coefficient of adhesion. The tires of a steering axle that achieves a lateral friction utilization level of 1 are said to be saturated. Configuration performance is considered satisfactory if LFU is less than or equal to 0.80 (NRC recommended performance standard). Initially this performance measure was evaluated on a high friction surface. This measure was modified by evaluating LFU on low friction surfaces, which are more critical for steering performance, by using low friction tire characteristics (μ=0.2). This performance measure was evaluated using the same manoeuvre as FD.
Low Speed Offtracking (LSOT) was measured as the maximum lateral displacement of the centre-line of the last axle of the configuration from the path taken by the centre of the steer axle. Configuration performance is considered satisfactory if LSOT is less than or equal to 5.6 m (TAC performance standard). This performance measure was evaluated using the same manoeuvre as FD and LFU.
High Speed Steady State Offtracking (HSOT) was measured as the maximum lateral displacement of the centre-line of the last axle of the configuration from the path taken by the centre of the steer axle. Configuration performance is considered satisfactory if HSOT is less than or equal to 0.46 in (TAC performance standard). This value represents a minimal clearance of 0.15 m between the trailer tires and the outside of a 3.66-m wide conventional traffic lane. This performance measure was evaluated when the vehicle is operated in a 393-m curve radius, at a speed of 100 km/h, thereby attaining a steady lateral acceleration level of 0.2 g.
Transient Offtracking (TOT) was measured as the maximum lateral displacement of the centre-line of the last axle of the configuration from the path taken by the centre of the steer axle. Configuration performance is considered satisfactory if TOT is less than or equal to 0.8 m (TAC performance standard). This performance measure was evaluated in the same manoeuvre as LTR and RWA.